1. Field of the Invention
The present invention relates to a protection diode for protecting the gate oxide film of the MOS field effect transistor (hereinafter referred to as MOSFET) from surge breakdown.
2. Background Art
In general, the thickness of a gate oxide film used in the MOSFET is several tens of nanometers. Therefore, when a surge is inputted into the gate and the gate voltage reaches several kilovolts, the gate oxide film is broken down. For preventing this, a protection diode to discharge a surge is inserted in the gate. As protection diodes, not only vertical diodes, but horizontal diodes have been used (for example, refer to Japanese Patent Laid-Open No. 2009-238973). As a horizontal protection diode, there is a horizontal bidirectional diode wherein a P-type gate side diffusion layer, an N-type well layer, and a P-type grounding side diffusion layer are transversely arrayed on a semiconductor substrate.